1. Field of the Invention
The present invention relates generally to devices for perforating sheets of paper for insertion in loose-leaf ring binders and, more particularly, to a paper punch for use in combination with a loose-leaf notebook or a ruler.
2. The Prior Art
Devices for perforating sheets for insertion in loose-leaf ring binders and adapted to be carried therein have been around for a long time. Faifer disclosed such a combined perforator and binder in 1915, see his U.S. Pat. No. 1,142,032. Improvements followed. See U.S. Pat. Nos. 1,567,643, granted to Hearne in 1925; 2,139,159, granted to Hammen in 1938, 2,370,319, granted to Lippincott in 1945; 2,495,687, granted to Belmont in 1950; and 3,172,325, granted to Wernham et al. in 1965, to name a few.
In a copending application Ser. No. 08/061,427, filed May 6, 1993, and assigned to a common assignee, Clix Products Inc., of Natick, Mass., there is disclosed a sheet perforating punch formed of hard polymeric material.
As known and as exemplified by the patents referred to above, it is advantageous to have a perforating device which is designed to be carried in a loose-leaf ring binder so that papers intended to be inserted therein can be punched immediately prior to insertion.
Most, if not all, perforating devices excepting the one disclosed in said copending application, were formed of metal for accurate long lasting punching use. As known, paper punches formed of plastic, as in said copending application Ser. No. 08/061,427, tend to wear rapidly as between the punch teeth and their corresponding die holes unless very strict registration is maintained therebetween. Maintaining such strict registration is and remains a difficult task, however. This problem is especially acute with respect to all plastic sheet perforating punches of present design in which the male punching member is designed to enter, from the top and at a slight angle, its corresponding female die hole.